1. Andrea Attenasio, DO Orthopaedic Surgery Resident – Division of Orthopaedic Trauma & Adult Reconstruction, Department of Orthopaedic Surgery Cooperman Barnabas Medical Center/Jersey City Medical Center – RWJBarnabas Health, Livingston, NJ/Jersey City, NJ 
2. Pasquale Gencarelli Jr BS – Division of Orthopaedic Trauma & Adult Reconstruction, Department of Orthopaedic Surgery Cooperman Barnabas Medical Center/Jersey City Medical Center – RWJBarnabas Health, Livingston, NJ/Jersey City, NJ 
3. Nikki A. Doerr DO – Division of Orthopaedic Trauma & Adult Reconstruction, Department of Orthopaedic Surgery Cooperman Barnabas Medical Center/Jersey City Medical Center – RWJBarnabas Health, Livingston, NJ/Jersey City, NJ 
4. Alex Tang MD – Division of Orthopaedic Trauma & Adult Reconstruction, Department of Orthopaedic Surgery Cooperman Barnabas Medical Center/Jersey City Medical Center – RWJBarnabas Health, Livingston, NJ/Jersey City, NJ 
5. Frank A. Liporace MD – Division of Orthopaedic Trauma & Adult Reconstruction, Department of Orthopaedic Surgery Cooperman Barnabas Medical Center/Jersey City Medical Center – RWJBarnabas Health, Livingston, NJ/Jersey City, NJ 
6. Richard S. Yoon MD – Division of Orthopaedic Trauma & Adult Reconstruction, Department of Orthopaedic Surgery Cooperman Barnabas Medical Center/Jersey City Medical Center – RWJBarnabas Health, Livingston, NJ/Jersey City, NJ 
7. Jaclyn M. Jankowski DO – Division of Orthopaedic Trauma & Adult Reconstruction, Department of Orthopaedic Surgery Cooperman Barnabas Medical Center/Jersey City Medical Center – RWJBarnabas Health, Livingston, NJ/Jersey City, NJ 

ABSTRACT

Introduction
The amount of reverse total shoulder arthroplasty (rTSA) procedures performed is expected to increase as indications expand and outcomes continue to improve. However, the use of cemented or cementless humeral stems for the treatment of rotator cuff (RTC) arthropathy and complex proximal humerus fractures (PHF) is an area of ongoing debate. The purpose of this study was to examine and compare survivorship, functional outcomes, and complication rates between cemented and cementless humeral stems during rTSA in the treatment of RTC arthropathy and complex PHF. 

Methods
A retrospective review of consecutive patients undergoing rTSA performed at a single academic medical center between 2018 and 2020 was conducted with a minimum follow-up of 2-years. Patients were separated into two groups for comparative analysis (cemented versus cementless stems). Patient demographics, comorbidities, operative data, range-of-motion (ROM), and functional outcomes such as the Quick Disabilities of the Arm, Shoulder, and Hand (qDASH) were collected and evaluated. A Kaplan-Meier survival curve with log-rank tests was utilized to analyze and compare survivorship, defined as reoperation or implant failure, between the two groups.

Results
Forty-eight patients were identified. Twelve (25%) patients received a cemented humeral stem while 36 (75%) did not. Average follow-up was similar between the two groups (3.0 ± 0.6 vs 3.0 ± 0.7 years, p=0.91). Cemented stems were used in more patients treated for PHFs while cementless stems were used more in patients treated for RTC arthropathy (p<0.002). Patients in the cemented group had greater qDASH scores vs. patients in the cementless group at baseline (78.2 ± 11.7 vs. 67.6 ± 11.3, p=0.008) and at latest follow-up (31.6 ± 19.3 vs 21.4 ± 12.4, p<0.04), but did not have significantly improved delta scores (46.6 ± 12.4 vs 46.2 ± 14.2, p=0.93). ROM was increased in all measured planes and continued to improve at 3-month, 6-month, 12-month, and 24-month follow-ups for both groups. There were no significant differences noted in the change of ROM at most time points; however, there were significantly greater improvements for flexion/extension (p=0.009) and abduction/adduction (p=0.004) at the 2-year follow up in the cementless stems. Lastly, the cemented group trended towards having higher reoperation rates vs. the cementless group (25% vs 8%, p=0.16). A Kaplan-Meier curve also demonstrated similar trends for survivorship up to 4-years, although these findings did not reach statistical significance (74.1% in the cemented group vs 91.7% in the cementless group, p=0.11).

Discussion
In rTSA for RTC arthropathy and complex PHF, cementless humeral stems provide similar survivorship and complication rates with slightly improved flexion/extension and abduction/adduction at latest follow-up when compared to cemented stems. Moreover, cementless humeral stems trended towards lower reoperation rates and greater survivorship at 4-years postoperatively, albeit not significant. Future randomized control trials with longer follow-up times are required to confirm these findings.

Keywords: Reverse total shoulder arthroplasty; rTSA; Cemented; Uncemented; Humeral stems

INTRODUCTION
Total shoulder arthroplasty (TSA) attempts to achieve a painless and functional shoulder joint with approximately 11,000 procedures performed in North America annually (6). Most recently, reverse total shoulder arthroplasty (rTSA) has gained popularity as indications expand from elderly patients to include younger, more active patients (9,12). Some indications include rotator cuff (RTC) arthropathy, complex proximal humerus fracture (PHF), tumor resection, revision arthroplasty, and rheumatoid arthritis (12). The rTSA technique has rapidly evolved as a result of improved understanding of anatomy as well as technological advances in implant design as a solution in patients with potential rotator cuff compromise (4,9). Components have been redesigned in an effort to improve patient outcomes (6). Some propose that the method of humeral stem fixation correlates with stability and that a durable stem is paramount to preventing complications such as dislocation and loosening (3,9). 

Fixation of the humeral stem may be achieved by either cement or cementless components, depending on the shoulder pathology and surgeon preference (6). Historical studies investigating outcomes in anatomic shoulder arthroplasty advocated for cemented fixation due to improved outcome scores, strength, and range-of-motion (ROM) when compared to cementless fixation group (6). Early rTSA procedures typically employed a cemented humeral component with satisfactory outcomes; though, utilization of a cementless technique has been reported to offer distinct benefits such as simplified operative technique, avoidance of cement-related complications, greater ease of revision, and long-lasting biologic fixation (6,12). Studies looking at loosening of the humeral stem found no difference in rates of aseptic loosening between cemented or non-cemented stems (2). Higher rates of loosening were found with longer follow up as well as in patients undergoing rTSA for tumor resection or revision arthroplasty. Recent trends demonstrate that cemented humeral fixation is utilized more commonly for proximal humerus fracture, while cementless is preferred for other indications such as RTC arthropathy (11,12). 

While rTSA is a reliable surgical option for arthritic shoulder pathology and in the setting of fracture, more comparative studies regarding humeral stem fixation types may significantly contribute to concepts reported in current literature (8). The purpose of this study was to analyze and compare survivorship, functional outcomes, and complication rates between cemented and cementless stems during rTSA for RTC arthropathy and complex PHF. 

MATERIALS and METHODS
After receiving approval from our Institutional Review Board, a retrospective review of consecutive patients undergoing rTSA performed at a single academic medical center between March 2018 and March 2020 was conducted. Two fellowship-trained orthopedic surgeons performed the operations in this study. Inclusion criteria were as follows: (1) age ≥ 18-years-old, (2) rTSA in the setting of a proximal humerus fracture or rotator cuff arthropathy, (3) use of cemented or cementless humeral stems, and (4) minimum follow-up time of 2-years. Exclusion criteria included patients that (1) did not meet inclusion criteria, (2) patients with previous surgical shoulder interventions, or (3) surgical treatment with techniques other than rTSA. 

Patients were separated into two groups for comparative analysis (cemented versus cementless stems). More importantly, patients were not randomized into either study group and initial treatment was determined primarily based on surgeon preference. Data collected included patient demographics, comorbidities, operative data, range-of-motion (ROM), and functional outcomes such as the Quick Disabilities of the Arm, Shoulder, and Hand (qDASH). A KaplanMeier survival curve with log-rank tests was utilized to analyze and compare survivorship, defined as reoperation or implant failure, between the two groups. 

Rehabilitation Protocol 
The postoperative rehabilitation protocol for both groups was adjusted at the discretion of the treating surgeon based on the quality of the repair and robustness of the soft tissue. However, protocol progression generally occurred in 4 phases (0-2 weeks, 2-6 weeks, 6-16 weeks, and 1624 weeks). During the first 2 weeks, patients were placed in a shoulder immobilizer with an abduction pillow and made non-weight bearing with no ROM of the shoulder. Patients were allowed hand/wrist/and elbow motion as tolerated and encouraged to use ace wrap for swelling.      In weeks 2-6, PHF patients remained non-weight bearing, but were allowed to remove the shoulder immobilizer with abduction pillow for exercises only. However, for elective patients that underwent rTSA for RTC arthropathy, were permitted weight bearing of up to 5lbs at the discretion of the treating surgeon. Home exercise/physical therapy included active range-of-motion (AROM), active-assisted range-of-motion (AAROM), and passive range-of-motion (PROM) of forward elevation in the plane of the scapula, internal rotation to the abdomen, and external rotation to neutral. Shoulder extension past the midaxillary line was not permitted. Patients were encouraged to start weaning use of the shoulder immobilizer and abduction pillow while they slept at weeks 5-6. 

By weeks 6-16, patients were made weight-bearing as tolerated and AROM/AAROM/PROM progressed to all planes. Concentric/eccentric exercises, plyometrics, closed chain strengthening exercises, and proprioception activities were begun. Lastly, at 16-24 weeks, patients were allowed to gradually return to full activities and instructed to continue home exercise strength and endurance programs.

Statistical Analysis
Descriptive data were reported as means ± standard deviation (SD) for continuous data or counts (%) for categorical data. Independent t-tests were used to compare means between continuous variables and chi-squared or Fisher exact tests were used to compare counts for categorical data. A Kaplan-Meier survival analysis was used to determine survivorship for cemented and cementless implants, defined as implant failure or reoperation. A log-rank test was used to compare survival curves between the two groups. A p-value ≤0.05 was considered to be statistically significant. All statistical analyses were performed using SPSS version 25 (IBM Corporation, Armonk, New York).  

RESULTS 
Forty-eight patients were identified that met inclusion criteria. Twelve (25%) patients received a cemented humeral stem while 36 (75%) received a cementless, press-fit stem (Table 1). There was no statistical difference in the demographic makeup of the cemented and cementless groups. The mean age was 70.4±8.5 years in the cement group and 66.8±11.6 years in the cementless group (p=0.33). Average body mass index in the cement group was 28.5±7.1kg/m2 and 31.5±7.1kg/m2 in the cementless group (p=0.21) respectively. Nine females (75%) were included in the cemented group while the cementless included twenty-four (67%) (p=0.73). Average follow-up was similar between the two groups (3.0±0.6 years vs. 3.0±0.7 years, p=0.91). Cemented stems were used in more patients treated for PHFs while cementless stems were used more in patients treated for RTC arthropathy (p<0.002).  

The cemented group trended towards having higher reoperation rates vs. the cementless group although these findings were not significant (25% vs. 8%, p=0.16) (Table 2). Patients in the cemented group had greater qDASH scores vs. patients in the cementless group at baseline (78.2±11.7 vs. 67.6±11.3, p=0.008) and at latest follow-up (31.6±19.3 vs. 21.4±12.4, P<0.04), but did not have a significantly improved change in qDASH scores over time  (46.6±12.4 vs. 46.2±14.2, p=0.93) (Table 3). ROM in both groups was increased post-operatively in all measured planes and continued to improve at 3-month, 6-month, 12-month, and 24-month follow-ups. While there were no significant differences in the change of ROM between both groups, of note, the cemented group demonstrated a significantly greater change in flexion (p=0.009) and abduction (p=0.004) between 6 months and 1 year. A Kaplan-Meier curve also demonstrated similar trends with increased survivorship up to 4-years in the cementless group, although these findings also did not quite reach statistical significance (74.1% in the cemented group vs. 91.7% in the cementless group, p=0.11) (Table 4) (Figure 1). 

DISCUSSION
According to the data in this study, patients with cemented stems had higher qDASH scores at baseline (78.2±11.7 vs. 67.6±11.3, p=0.008) and at latest follow-up (3.16±19.3 vs. 2.14±1.24, P<0.04) compared to those with cementless stems. Most of the patients undergoing cemented fixation occurred in the setting of PHF while cementless occurred mostly for RTC arthropathy. Fractures, being acute in nature, were more likely to undergo surgery less than or equal to 4 weeks from the time of injury (67% vs 31%, P=0.04) compared to the chronicity of RTC arthropathy. This could possibly explain the trend in overall higher qDASH scores in the cemented group. Compared to patients with acute fractures, patients with chronic RTC arthropathy may be more deconditioned due to the prolonged impact of their condition, as reflected in their lower pre-operative qDASH scores. Overall, there was no statistical difference between the change in scores, thus indicating that each surgical technique is able to achieve similar clinical improvement. These findings are consistent with the current literature comparing both humeral stem fixation methods for rTSA performed for various indications (5,8,9) as well as studies looking specifically at rTSA for PHFs (5,10,11). Mazaleyrat et al. (8) reported improved post-operative clinical outcome scores in patients undergoing rTSA regardless of fixation method as well as no significant difference in overall clinical outcomes between the cemented and cementless groups.

Mazaleyrat et al. (8) also found improvement in active joint ROM post-operatively regardless of fixation method, though there was a significant increase in flexion and abduction in the cemented group (p<0.001, p<0.006). The improvement in ROM demonstrated by patients in each cohort of this study was consistent with these findings, and no difference in the change in ROM between the cemented and cementless groups was observed, except for a significantly greater change in flexion and abduction in the cemented group compared to the cementless group between 6 months and 1 year (p=0.009 and p=0.004, respectively). A retrospective study by Wright et al. (12) evaluating the outcomes of cementless stems for rTSA in the setting of PHFs demonstrated an average forward flexion of 130 ± 31 degrees and external rotation of 32 ± 18 degrees which is comparable to the flexion and external rotation achieved by the cementless cohort in this study at 2 years (127.5±28.8 degrees and 49.2±18.9 degrees, respectively). Other studies directly comparing cemented and cementless stems have also shown no difference in outcome scores or ROM between the two groups (5,7,9). The findings of this study are consistent with the current literature reporting that cemented and cementless humeral stems for rTSA achieve similar clinical outcome scores and ROM post-operatively.

In terms of complications, the cemented group trended towards having higher reoperation rates when compared to the cementless group, although these findings were not significant (25% vs. 8%, p=0.16). A Kaplan-Meier curve also demonstrated similar trends for survivorship up to 4 years, with the cementless group having improved survivorship, although these findings also did not reach statistical significance (74.1% in the cemented group vs. 91.7% in the cementless group, p=0.11). The use of cemented implants has historically been indicated in osteoporotic bone or in the setting of fracture, as there is reduced risk of iatrogenic fracture. Yet, the use of cementless components offers several advantages including a significantly lower incidence of post-operative fractures of the acromion, less operative time, and ease of revision when compared to cemented shoulder arthroplasty procedures(9). Additionally, cementless components avoid of the risk of several complications observed with cement use such as osteoblast cytotoxicity secondary to exothermic reactions and methyl methacrylate monomers, cardiopulmonary collapse reported in hip and knee literature associated with pressurized cementing techniques as well as neurologic injury due to extravasation (4,6,12). Cemented stems have also reportedly been associated with other complications such as a greater relative risk of nerve injury, infection, and thromboembolism (9).

A systematic review performed by Phadnis et al. (9) comparing cemented and cementless fixation found that overall cementless stems have equivalent clinical and radiographic outcomes with less potential complications. Similarly, a recent study demonstrated that cemented stems are associated with increased rate of radiolucent lines and osteolysis, which has the potential to lead to increased pain and need for revision surgery. This study also reported that cementless stems were more prone to internal stress shielding (1). Another systematic review with a meta-analysis found that there was no difference in rate of aseptic loosening between cemented and cementless groups; however, radiolucent lines were more common in cemented stems (2). The study also found a trend for increased aseptic loosening in cohorts with longer follow up, but there was no significant difference in aseptic loosening based on stem fixation method. The results of this study regarding survivorship trends, in conjunction with previously reported data, empha the importance of longer term follow up to monitor for signs of loosening.

Limitations to this study include its retrospective nature and small cohort. This study additionally includes patients undergoing rTSA for differing indications, with the propensity for cemented technique use in patients with PHFs and a cementless technique in cases of RTC arthropathy. The objective ROM data was only available up to the two-year postoperative follow-up. To provide a more definitive comparison of the cemented and cementless groups, longer term prospective studies are needed with a larger cohort. This may help better characterize the survivorship of the different types of stem fixation and potentially identify significance in the trend towards higher reoperation rates in the cemented group. Additionally, future studies may benefit from conducting a granular analysis of cemented vs. uncemented in patients undergoing rTSA for RTC arthropathy and for PHFs with comprehensive radiographic evaluation to assess for any implant migration, mechanical loosening, or osteolysis at each follow-up timepoints.

CONCLUSION
The evolution of rTSA procedures has developed a functional solution to shoulder pathologies such as rotator cuff arthropathy and complex four-part proximal humerus fractures associated with rotator cuff compromise as well as to patients deemed poor surgical candidates for alternative fixation.  The data presented in this study is consistent with other recent literature and suggests that the utilization of cementless humeral prosthesis may lead to equivocal clinical outcomes with improved ROM and the potential for lower reoperation rates with longer implant survivorship in the setting of both PHFs and RTC arthropathy. Development of a larger, randomized trial with long term follow up is warranted to further assess the potential benefit of using a cementless technique in both the setting of complex PHFs and RTC arthropathy.

Figure 1 | Figure 2 | Figure 3 | Figure 4 | Figure 5 | Figure 6 | Figure 7 | Figure 8 | Figure 9 | Figure 10 | Figure 11

FIGURE LEGEND
Figure 1. Survival curve comparison between cemented and cementless humeral stems represented in years. Log-rank p=0.11

REFERENCES

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